1. Field
The present disclosure generally relates to motor control, and more particularly relates to permanent magnet or interior permanent magnet motor control.
2. Description of the Related Art
The permanent magnet (PM) synchronous motor possesses many appealing characteristics for various applications, including pure-electric or hybrid-electric vehicles. The maximum input power of a vehicle is dictated, in part, by the size of the power sources (i.e., battery, fuel cell engine, supercapacitor, etc.). Direct current (DC) power is the product of the DC voltage and DC current. Quite often, the DC bus voltage varies with motor output power (i.e., Torque*Speed). As a result, rapid changes in vehicle load may cause large fluctuations in the DC bus voltage.
Traction electric motors may be used to propel electric or hybrid vehicles. A traction electric motor drive is often required to perform over a wide operating range. Typically the operating range of an electric machine, such as the traction electric motor, is divided into two regions: a constant torque region and a constant power region. It is important to maintain the ability to change quickly and smoothly between the constant torque and constant power modes of operation.
Interior permanent magnet (IPM) synchronous motors are also used in electric vehicle traction drives due to their positive features such as high efficiency and high power density. Such applications require the motor drives to work in a wide speed range and constant power while maintaining high efficiency. In the high speed range, or in field-weakening mode operation, the optimal motor current commands are not only a function of speed and requested torque, but also a function of various motor parameters, DC bus voltage and motor temperature.
Existing PM or IPM motor control methods and apparatus, particularly in electric or hybrid vehicle applications, may perform poorly when the DC bus voltage varies. Rapid fluctuation of the DC bus voltage, for example due to rapidly changing power demands, exacerbates this problem, and existing PM or IPM motor control systems and methods are typically unable to adequately compensate. Furthermore, due to the multiple optimal curves and boundaries imposed on the motor current commands, simple regulators that can control the motor torque output precisely and quickly in the high speed and/or the field weakening operating regions do not appear to be available. Accordingly, a control system method and apparatus is desirable.